Multi-ply dispersible nonwoven material

ABSTRACT

The invention relates to a nonwoven material having sufficient strength to be used in a pre-moistened state but also having dispersibility properties which allow the product to be flushed. The material comprises at least two nonwoven webs, at least one of which is hydroentangled. Each of the individual webs has a basis weight of 20-100 gsm. The nonwoven webs are joined together by thermal or mechanical embossing, or a combination of these.

FIELD OF THE INVENTION

The present invention relates to products which are flushable, that is disposable through a water closet system without risk of clogging sewer pipes. More particularly, the present invention relates to a nonwoven material having sufficient strength to be used in a pre-moistened state but also having dispersibility properties which allow the product to be flushed.

BACKGROUND

Ordinary toilet paper is designed for use in the dry state, and when flushed down the toilet it is readily disperses so as to flow down a properly draining sewer system without causing any blockage. A moist tissue such as products used for e.g. baby care and personal hygiene must necessarily have further properties in order to be useful in the wet state in which they are delivered. These products must also be maintained in their pre-moistened state for a considerable time between manufacture and use. However, for obvious reasons it is often desirable to dispose of used wet wipes by flushing them down the toilet.

In order to provide sufficient wet strength in pre-moistened wipes, a wet strength agent is often added. Such agents may be a cause of insufficient disintegration properties. Though wet strength agents and water soluble adhesives at some point dissolve in water, the dispersibility of the product may not be fast enough to eliminate blockage risks. Another approach to dispersability is the use of various fiber length compositions. Short fibers may provide good dispersability but do not provide the desired surface and “feel” characteristics that are required in wipes. Long fibers again are prone to accumulating on screens and the like in sewer systems, again leading to blockage problems.

In EP 0 904 933 is disclosed a water-disintegratable wiping sheet comprising two webs both containing pulp fibers but of different composition, one web comprising water-swellable binder.

In EP 2 627 229 is disclosed a moist wipe or hygiene tissue which has good strength properties and is readily dispersible. The product comprises a hydraulically entangled nonwoven material impregnated with a wetting composition and has a defined composition of pulp and man-made and/or natural fibers; and it comprises at least two plies of nonwoven material held together by frictional forces without mechanical bonding or adhesive.

In EP 2 148 950 is disclosed a dispersible nonwoven web having at least three layers of specified compositions of short and long fibers, and comprising a triggerable binder, the binder being one that is not soluble in the wetting composition but is dispersible or soluble in the aqueous conditions encountered in the flushing situation.

In U.S. Pat. No. 8,603,297 is disclosed a dispersible wet wipe comprising at least a first layer which is preferably an uncreped air dried tissue web, and a second layer which may be a nonwoven web. The material further comprises a triggerable binder and a wetting composition.

In U.S. Pat. No. 7,838,725 is disclosed a dispersible absorbent product having a mechanically weakened multi-layered structure comprising at least two layers joined together in a staggered manner such that the mechanically weakened regions are not directly superimposed over each other. The layers may be joined by applying pressure and/or heat, using adhesives or e.g. using ultrasonic bonding.

In U.S. Pat. No. 8,241,743 is disclosed a nonwoven web comprising man-made fibers and pulp fibers, the former having a given proportion of fibers of a given length; and the web is weakened by providing compressed regions forming lines of weakness, causing the web to fail when subjected to defined stresses.

In U.S. Pat. No. 9,314,142 is disclosed a dispersible multilayer wipe material based on the combination of cellulosic fiber, bicomponent fiber and a binder.

EP 1320458 also discloses the use of bicomponent fibers. These bicomponent fibers are hydroentangled first with wood pulp and synthetic fibers and then thermally fused at elevated temperature to increase the strength.

Some of these moist toilet tissue materials were designed to have sufficient wet strength for use and for dispensing. In order to have that strength, the material may include synthetic fibers. However, those fibers are longer in length as compared to wood pulp which causes problem of clogging, inefficient dispersion, and takes a longer time for full dispersion apart from the higher cost of those fibers.

Ion-sensitive water dispersible polymer provides in-use strength and disperses in water. However, the dispersion of binder is highly dependent on the water hardness and temperature. Moreover, salt sensitive lotion and binder can be harmful to the skin.

SUMMARY OF THE INVENTION

The present invention provides a dispersible nonwoven material which avoids the use of binder and oil-based synthetic fiber. The material comprises at least two nonwoven webs, at least one of which is hydroentangled. Each of the individual webs comprise 50%-95% wood pulp and 5%-50% of short cut man-made fibers and/or natural fibers and has a basis weight of 20-100 gsm. Each individual nonwoven web is highly dispersible because of its low basis weight. The nonwoven webs are joined together by thermal or mechanical embossing, or a combination of these. When the at least two nonwoven webs are joined together by thermal and/or mechanical embossing, the collective wet strength of the joined nonwoven web is higher than that of the individual nonwoven webs. The embossed, joined webs separate into individual webs after flushing and are again highly dispersible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an alternative method for preparing a nonwoven material according to an embodiment of the invention;

FIG. 2 shows a further alternative method for preparing a nonwoven material according to an embodiment of the invention;

FIG. 3 is a diagram showing the wet MD and CD strength profiles of various multi-ply webs joined together by thermal/mechanical embossing, with reference to Table 1, supra.

DETAILED DISCLOSURE

The material of the invention comprises at least two individual nonwoven web layers formed separately. At least one, preferably several of the webs is/are hydroentangled. The hydroentanglement is carried out using wet laid technology with a composition of 50%-95% wood pulp and 5%-50% short cut fibers and/or natural fibers. The short cut fibers of flushable wipes are man-made fibers which are non-thermoplastic. Non-limiting examples of short-cut man-made fibers useful in the dispersible nonwoven material of the invention are regenerated cellulose, lyocell, viscose rayon, polylactic acid and polyvinyl alcohol. The present invention avoids the use of any glass fiber and oil-based synthetic fibers such as polyester, nylon, polypropylene, polycarbonates, polyethylene, polyvinyl chloride, aramid, polyacrylate, and combinations thereof. The natural fibers might be cotton, hemp, flax, linen, bamboo, sisal, jute, kapok, etc. The fiber length of the short cut man-made fibers and/or natural fibers useful in the dispersible nonwoven material of the invention is in the range of 5 mm to 15 mm. Each individual nonwoven web preferably has a basis weight of 20 gsm to 100 gsm. Each individual nonwoven web preferably has a wet strength of 100 g/50 mm to 600 g/50 mm.

After hydroentanglement, the two nonwoven webs are dried (using e.g. drying cans) and then joined together by thermal or mechanical embossing. The thermal/mechanical embossing holds the two nonwoven webs together in the presence of the wetting solution. The composite web has a significantly higher strength than the individual webs. The joined embossed fabric material provides sufficient in-use and dispensing strength to the product, but splits into its component webs and disperses fast after flushing down with mild agitation in water. The dispersibility of the subject material is according to GD 3 guidelines; 50 to 100% pass through after 5 min.

The final basis weight for the nonwoven material according to the present invention is in the range 40 to 120 gsm. Preferably, the wet strength in the conditions of use of the nonwoven according to the present invention is greater than 250 g/50 mm.

Thermal embossing for the purpose of the present invention may advantageously be carried out at a pressure in the range of 40 to 90 N/mm², using an embossing bonding area of 5% to 33% with continuous or discontinuous pattern, and a temperature range of 140° C. to 180° C. Preferably, the embossing pressure may be about 60 N/mm², and the temperature about 160° C. Preferably, the bonding area is greater than 5%.

Embossing without elevated temperature can advantageously be carried out for the present invention with a pressure of 60 to 160 N/mm² and embossing bonding area of 5% to 33% with a continuous/discontinuous pattern.

To prepare wet wipes, the nonwoven fabric material according to the present invention is treated with a wetting liquid. Advantageously, the wetting liquid may comprise about 98% water and about 2% preservative, for example Lonza Geogard 221. Preferably, wetting liquid is used in an amount not exceeding 2.5 times the weight of the dry nonwoven material per unit area.

In general, the wetting liquid may further comprise additional agents such as emollients, viscosity modifier, natural or synthetic oil and fats, surfactants, antimicrobial agents, particulates, alcohol, salts, organic solvents, pharmaceutical agents such as dimethyl sulfoxide; odor control agents, detergents, silicones, fragrance, pH control agents, whitening agents and surface feel modifiers.

DESCRIPTION OF PREFERABLE EMBODIMENTS

FIG. 1 is a schematic representation of an embodiment of a process for preparing a nonwoven according to the present invention. Stock is prepared in a headbox 1 and a first web 2 is laid wet according to procedures known to the person skilled in the art. For example, the web is laid on a plastic wire running at a speed of 2 to 4 m/s (400-800 feet/min) and transferred to the hydroentangling station where the fibrous structure is entangled using high pressure water jets 3. The web is hydroentangled by 3 to 5 different consecutive nozzles with a water jet pressure of 2.75-5.5 MPa (400-800 psi) and laid on top of a second wet laid web 4 prepared in an analogous manner using second headbox 5 and high pressure water jets 6 but not necessarily using identical parameters. The combined web passes through drying station 7 and thermal or mechanical embossing station 8. The wet laid webs 2, 4 have a composition of 50-95% wood pulp fibers and 5-50% shortcut fibers. The proportion of shortcut fiber to wood pulp fiber depends on the type of shortcut fiber used. If the shortcut fibers are of flat cross-section and of short length, then a higher proportion of shortcut fiber is required, and if the fiber is of round cross-section and of long length, then the proportion of shortcut fiber will be low. Preferably, at least 20% of shortcut fiber is used.

An example of wood pulp fiber which may be used in a nonwoven according to the invention is Grande Prairie ECF Northern Bleached Softwood. An example of shortcut fiber which may be used in a nonwoven according to the invention is Danufil 1.7 dtex 8 mm from Kelheim Fibres GmbH, Germany. Cotton fiber is a further alternative to be used as shortcut fiber.

FIG. 2 shows another embodiment of a process for preparing a nonwoven web according to the present invention. The equipment shown includes headbox 9 and high pressure water jets 10, as well as drying station 11 and thermal or mechanical embossing station 12. A wet laid and hydroentangled web 13 is laid on another web 14 which is unwound from reel 15, being previously formed and entangled and pre-wound. The combined web is dried and embossed to form a nonwoven according to the present invention. Also two preformed and pre-entangled webs may be unwound and embossed to form a nonwoven material according to the present invention.

EXAMPLES

Prototype samples were prepared using two hydroentangled sheets produced separately at 30 and 40 gsm each with entanglement pressure of 400, 400, and 500 psi which are then thermally joined together at a temperature of 160° C. and a pressure of 60 N/mm², with a continuous pattern having embossing bonding area of 24.4%.

Table 1 shows the composition and ID (corresponding to FIG. 3) of the samples prepared.

TABLE 1 Various nonwoven webs with different fiber composition and basis weights Composition Sample ID 20% Short Cut Fiber, 80% Wood - 30 gsm A1 20% Short Cut Fiber, 80% Wood - 40 gsm A2 30% Short Cut Fiber, 70% Wood - 30 gsm B1 30% Short Cut Fiber, 70% Wood - 40 gsm B2 20% Short Cut Fiber, 80% Wood - 60 gsm C 30% Short Cut Fiber, 70% Wood - 60 gsm D 20% Short Cut Fiber, 80% Wood - 40 gsm - E No Entanglement 100% Wood Pulp - No Entanglement 35 gsm

In FIG. 3 are shown the wet MD and CD strength profiles of various combinations of the webs of Table 1 joined together by thermal embossing.

All the samples showed in FIG. 3 split into two separate webs after mild agitation in water and disperse fully (100% slosh box dispersion) after 5 min according to INDA/EDANA flushability GD3 guidelines. Table 2 shows the results.

TABLE 2 Slosh box dispersion results for samples in FIG. 3 Sample Id Slosh Box (% pass Through) - 5 min A1 + A1 99.93 A1 + A2 100.00 A2 + A2 99.52 A2 + E 100.00 A2 + 35 gsm tissue 99.94 B1 + B1 100.00 B2 + B1 99.79 B2 + B2 99.33 B2 + E 99.86 B2 + 35 gsm tissue 100.00 

1. A nonwoven fabric material comprising at least two nonwoven web layers, of which layers at least one is hydroentangled, where each individual nonwoven web layer has a basis weight of 20-100 gsm and each individual nonwoven web layer has a composition of 50%-95% wood pulp and 5%-50% short cut man-made fibers and/or natural fiber; and where the at least two nonwoven web layers have been joined together by thermal embossing, mechanical embossing or a combination of these.
 2. The nonwoven fabric material of claim 1, wherein the shortcut man-made fibers are selected from the group consisting of regenerated cellulose, lyocell, viscose rayon, polylactic acid and polyvinyl alcohol.
 3. The nonwoven fabric material of claim 1, wherein the natural fibers are selected from the group consisting of cotton, hemp, flax, linen, bamboo, sisal, jute and kapok.
 4. The nonwoven fabric material of claim 1, wherein the shortcut man-made fibers and/or natural fiber have a length in the range 5 mm to 15 mm.
 5. The nonwoven fabric material of claim 1, wherein the bonding area in the embossing is in the range 5% to 33%
 6. The nonwoven fabric material of claim 1, wherein the bonding area in the embossing is greater than 5%.
 7. The nonwoven fabric material of claim 1, further comprising a wetting liquid.
 8. The nonwoven fabric material of claim 6, comprising a wetting liquid in an amount not exceeding 2.5 times the weight of the dry nonwoven material per unit area.
 9. The nonwoven fabric material of claim 1, wherein the wet strength of the fabric material is greater than 250 g/50 mm. 